1. Field of the Invention:
The present invention relates to a method for purification of an amino acid using ion exchange resin, whereby the amino acid is contacted with the resin in countercurrent continuous multiple steps to greatly reduce the required amount of resin and the amount of water necessary for washing the resin.
2. Discussion of the Background:
Ion exchange resins have been widely used in purification and collection of highly pure amino acids from crude amino acid solutions industrially prepared by fermentation, synthesis and extraction. Serious problems involved in the use of ion exchange resin are that they require large amounts of resin and use large amounts of water. That is, where an amino acid is purified, it has been heretofore conventional to apply fixed bed operations using ion exchange resin. This technique comprises an adsorption step in which a fermentation broth of an amino acid having a pH adjusted to a specific value is contacted with a salt type, strongly acidic cation exchange resin layer, such as an ammonia type, etc. to adsorb the amino acid onto the resin layer. This step is followed by an elution step in which the amino acid is eluted with an eluent such as ammonia water, and the ion exchange resin is regenerated to a salt type.
When fermentation broth is passed through a conventional resin tower in the adsorption step, washing water is passed through after the fermentation broth in order to permit the fermentation broth to completely pass through the resin layer. In the elution step, washing water is passed after the fermentation broth in order to permit an eluent to completely pass through the resin layer. Furthermore, suspended substances in the fermentation broth are deposited in the resin tower during the adsorption step so that large amounts of washing water flowing in the reverse direction are needed to remove the deposit after completion of adsorption. This is not the only reason that water needs increase. The amount of water discharged during elution is large and facilities for treatment of the waste water become huge.
The amount of washing water increases as the amount of resin used increases. It is thus expected that by reducing the amount of resin used, the amount of washing water can be reduced and hence, facilities required for resin operations can be down-sized. Based on this expectation, various methods for reducing the amount of washing water used have been investigated (Japanese Patent Application Laid-open Nos. 50-127879, 52-11173 and 62-65690) but a considerable amount of washing water is still required.